This invention relates to a signal transfer system for a charge transfer device (hereinafter abbreviated CTD).
As an example of such a CTD, a charge coupled device (hereinbelow abbreviated CCD) employing three-phase or four-phase drive is known.
The CCD is constructed such that an input source electrode and an output drain electrode are provided in a substrate, a large number of transfer electrodes are arranged on the substrate between the source and drain electrodes through an insulating film, and three or four of the transfer electrodes constitute one stage. By successively applying three-phase or four-phase clock pulses to the transfer electrodes, charges in capacitors formed under the respective transfer electrodes are successively shifted and are fed to subsequent stages.
Such a CTD becomes a variable delay line by varying the clock frequency. The variable delay line can be used for compensating the time axis fluctuations of a recording appliance or equipment having a mechanical rotation system, such as video tape recorder and magnetic disc. When the CTD is operated by making the clock frequency during writing different than during reading, it can subject a signal to time compression or time expansion. Various applications of the CTD are considered in this manner, and for the time axis transforming operation as stated above, the clock must be frequency-modulated. When the clock frequency changes in this way, the transfer time of charges similarly changes. A change of the transfer time leads, in itself, to a change of the transfer efficiency. During the time axis transforming operation, the frequency characteristic changes with time. The operation has thus become inconvenient in the prior art.
The prior art has also had the disadvantage that a circuit for generating clock pulses corresponding to the respective clock frequencies becomes very complicated.